EP type rubbers, because of their superior resistance to ozone, to weathering and to heat, find extensive application to automotive parts, building components, industrial rubber products and the like. However, these rubbers tend to suffer from reduced roll retention and decreased tackiness prior to vulcanization, giving rise to processing problems.
By the term roll retention is meant the ability of an EP type rubber to adhere to the surface of a roll mill while being blended with additives. Insufficient roll retention contributes to laborious, time-consuming blending operation.
Tackiness is an adhesive property by which a rubber is bonded under mild pressure to a mating rubber or to a different material. Automobile tires and tubes are generally formed for instance by bonding rubber/rubber laminates into a desired shape which is subsequently vulcanized. Rubber laminates of poor tack strength are difficult to vulcanize while retaining the desired shape, and the resulting vulcanizate is susceptible to delamination.
To cope with these problems, a variety of tackifiers and processing aids have been proposed but with little success. Cumarone resins, terpene resins and aliphatic petroleum resins in common use as tackifiers would show no appreciable rise in tack strength. Extender oils if added in large amounts may improve tackiness to some extent, but would result in a vulcanizate being physically weak. Still much thus remains to be desired despite many attempts made with other tackifiers as disclosed for instance in Japanese Patent Publication No. 46-21897 and Japanese Patent Laid-Open Publication No. 51-87555.
The present invention seeks to provide an improved rubber composition which excels in roll retention and tack strength.